5 New Avalanche Statistics You Need To Know:

Bruce Temper, Director of the Utah Avalanche Center, recently cited this avalanche information resulting from new research into avalanche accidents. These numbers are heavy, shocking, and crucial. Please read them all, let them soak in, and use this information when you are in avalanche terrain.

Very large slab avalanche crown.

1. 47% of avalanche deaths occur when conditions are reported as “considerable.” Most weekend warrior backcountry skiers back off on their plans in avalanche danger points to high and extreme zones, but “considerable” conditions are harder to predict, and where almost half of all avalanche deaths occur. While the majority of ski tours that take place under these conditions will have a happy outcome, skills such as safe route-finding, keeping a handle on group dynamics, and knowing how to undertake a rescue and find buried victims is of paramount importance.

Heli avalanche control at Mt. Baker, WA. photo: grant gunderson

2. 49% of avalanche deaths in the U.S. are now snowmobilers. With the development of high-powered lightweight snow machines that are able to effortlessly glide over untracked snow, the number of snowmobilers heading into the backcountry is increasing each year. Route-finding, avalanche safety, and rescue skills are every bit as necessary, and a combination of the sled’s weight and motor power can trigger weak layers in the snowpack. Many snowmobilers utilize the same safety measures and carry the same technical gear (ABS-style “avalanche bags”, 457 kHz beacons, along with shovels, probes, and other rescue items) as backcountry skiers, but sleds can cover a lot of ground and generate a false sense of security.

Learn your avalanche anatomy.

3. 74% of all human-triggered slides occur on slopes between 34 and 45 degrees. Slopes in this range would generally be rated as upper intermediate or advance runs at a ski resort; in short, they’re the perfect pitch for powder skiing. Throughout the winter, snowfall will build up in layers with each passing storm. On steep slopes, fresh snow will slide during a storm and natural storm-cycle avalanches will reduce risk. On flat slopes, there simply won’t be enough pitch to trigger weaknesses in the layers. In this critical 34-to-45-degree zone, the weight of a passing skier or snowmobile will be just enough to cause a slope to collapse. Proceed with caution — even when in the trees.

Monster avalanche powder cloud.

4. Terminal velocity of an avalanche reaches over 150 kilometres per hour (93mph). That’s a lot faster than the speed limit on our provincial highways. If you think you can outrun an avalanche, well, you’re crazy. The air blast alone from the natural forces unleashed will knock you over and debris will almost instantly bury you.

Skier triggering avalanche. photo: garret grove

5. Wind can deposit snow 10 times faster than actual snowfall from storms. Most weather systems involve both precipitation and high winds. Wind will drive snow into sheltered parts of the mountain in many different directions during a storm and deposit significantly more snow in places such as gullies and on leeward slopes.

Small, skier triggered avalanche.

Bruce Tremper Bio:

Bruce has been the Director of the Forest Service Utah Avalanche Center since 1986. Bruce grew up in the mountains of western Montana where his father taught him the basics of avalanches at the age of 10. After a successful 15-year ski racing career, he did avalanche control at Bridger Bowl Ski Area in Montana, earned a Masters Degree in Geology from Montana State University, studying under the well-known avalanche scientists Dr. John Montagne and Dr. Bob Brown. He then took over as the Director of Avalanche Control at Big Sky Ski Area in Montana and worked as a backcountry avalanche forecaster for the Alaska Avalanche Center. Bruce has been featured in a number of national and international television documentaries about avalanches including those produced by National Geographic, Discovery Channel and PBS as well as appearing on a number of national network news programs. Bruce wrote the book “Staying Alive in Avalanche Terrain,” published by Mountaineers Books, now in its second edition. – Utah Avalanche Center

Bruce Temper. photo: utah avalanche center

Thanks, Bruce.

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Comment(s): 27

I discovered something. I was caught in a big sluff, maybe 40′ across, still standing on my skis making a turn. I thought nothing of it, as the snow was only about 8″ deep and it was moving slowly when it fractured. soft snow slide. so I didn’t really try hard to ski out to the side which I could have done right at the start. but as it carried me it gathered more and more snow and increased speed. I hadn’t figured on that, and soon it was too late to ski out and I was knocked down and took quite a ride, over a cliff band and into a gulley. got lucky. lesson learned: the slide gets bigger and faster as it goes; best chance to do things is right at the start.

I hate the bag of vague, crappy (government bureaucratic) words they use including ‘considerable’. how about making it more user friendly: safe or dangerous, ’cause that’s how it its. many Squaw lifer’s have said this for years.

They don’t say safe or unsafe because, like everything else, It is never that black and white. If your understanding of snow is yes or no, you should be cautious and always play it safe. If you are capable of reading terrain and understanding that any time your on a slope of the appropriate angle you are taking a risk, then you can use those assessments to make the risk a calculated one. Avalanches are tricky beasts. We don’t fully understand them, and most people that put themselves in harms way aren’t even aware of the things we do understand. I’ve taken numerous risks in the time I’ve snowboarded. I am ok with the risks I’ve taken, and don’t regret the lines I’ve enjoyed. I have no desire to die in an avalanche. I want to live a long happy life, but I am willing to take a calculated risk in order to make sure that happy part doesn’t fall to the sidelines. If you don’t understand that this is how the back country works, than you shouldn’t be there.

A lot of avalanche forecasters (Including Mr. Temper) hate the “considerable” term as well. Low, Moderate, High, Extreme are all pretty clear, but considerable is confusing. Safe or Dangerous is too cut and dry, because even a Low or Moderate day can be dangerous.

“Considerable” is kind of a nebulous term… Even at low and moderate designations you still need to “consider” the possibility of a slide in any conditions. I get that it’s an adjective, but there’s always room for a substitute if it doesn’t work for you.
A quick synonym search got me a quick list (searching “considerable”) and out of the group I think my favourite is “Substantial.”
“What are the avvy conditions like out there?”
“Substantial.”
Works for me.

Hey Tim, this information was written by Bruce Tremper. All Bruce’s info is in the article and you can go to the Utah Avalanche Center to find out more. Many media outlets have used his words over the years. He works for a non-profit organization and we wants to get these words out there to advance avalanche education. thanks.

I would love to hear statistically how many avalanches take place within the first 24 hours after a storm. I would guess up near 90%. It used to be that it was too fresh and too deep to venture into the backcountry on sleds without giving the snow at least a day to settle out after a storm cycle. Now that sleds have improved to such an incredible level, people are able to get themselves into way too much trouble immediately after a fresh dump of snow without giving that new layer a chance to bond to the previous layer. I can’t emphasize enough how important it is to educate yourself and to practice safe travel in the mountains. I’m more afraid these days of what other people are doing around and above me than anything else.

It depends where you are though, there are different conditions in different areas. For example, in Norway, there is almost always depth hoar in areas of the high mountains which persists the entire season. This type of avalanche is less dependent on loading from new snow and may be triggered even when upper layers are well bonded.

In areas with stronger sunlight then the percentage of human triggered avalanches 24-48 hours after a storm would be around the figure you stated.

Man I wish it was that simple in CO. I grew up in AK and remember how nice it was to be able to ride super steep lines a few days after a storm. Sadly that doesn’t happen here, and people get spanked long after a storm slab has settled. We have deep persistent week layers all season, almost every season. Those layers combined with our shallow snow pack, and large numbers of inexperienced riders have made CO one of the most avalanche accident prone regions in North America. We don’t usually get to touch the steeps until late spring. Its frustrating and easy to see why people take more risks.

The forecasters are there own worst enemy on this one. Although they have gotten better, for a very long time their forecasts lagged the real time by close to 24 hours. In other words they were prone to error on the side of caution, which damaged their credibility and tended to lead the more cynical to false conclusions. As the forecasts became more accurate in their timing, some users took awhile to catch on and others still think the avi agencies error on the side of conservative.

#5 played a major difference in accidents in the Wasatch last weekend. Wind loading tipped the snowpack just enough to make some substantial slides go. Luckily there were only close calls and no fatalities.

The editor cut off one of my sentences – what I meant to (fully) say is:

Great article, thanks. But I have always wondered about statements like #3. (74% of all human-triggered slides occur on slopes between 34 and 45 degrees. On steep(er) slopes, fresh snow will slide during a storm and natural storm-cycle avalanches will reduce risk.) I think the data on this is probably biased towards where people ski most. While there are a lot of people in the BC out skiing slopes under 34 deg, there are probably relatively few skiing slopes greater than 45 deg. So, it seems like a false conclusion to say that just because few people are ever caught in slides above 45 degrees, that this is due to the snow sluffing off there before anyone gets to it. On a day with avalanche hazard, I’d probably be just as spooked to be on a 50 degree slope as a 40 degree one. I totally agree with the flip side, though, that it would be safer to be on a 25-30 degree slope than a 40 degree one on such a day.